It is the long range purpose of this work to clarify the mechanism of cell transformation by studying the genetic, biological, and biochemical factors affecting carcinogenesis by chemical carcinogens. This work also aims to clarify the role of these factors in the etiology of human cancer incidence. The topics of present interest are: (1) the effects of physiological conditions of cells on the transformation; (2) the mechanism of fixation of transformation, in particular the role of DNA repair; and (3) the characterization of cell variants which shows the different sensitivity to chemical transformation. BIBLIOGRAPHIC REFERENCES: Dingman, C.W. and Kakunaga, T.: DNA strand breaking and rejoining in response to ultraviolet light in normal human and xeroderma pigmentosum cells. Int. J. Radiat. Biol. 30: 55-66, 1976.